The present invention relates generally to a cyclic electrophotographic copying process comprising the steps of producing a charge pattern by electrostatically charging and exposing a recording element, rendering a toner image visible with a pigmented developer liquid, and transmitting the image to an image-receiving material. More particularly, the invention relates to a copying proces wherein the surface of the recording element is cleaned with developer liquid before submission to a new copying cycle.
DE-AS No. 21 36 998, herein incorporated by reference, discloses an arrangement for producing electrophotographic copies by electrostatically charging the photoconductive layer of a recording element at each copying cycle, exposing the recording element to produce a latent charge image, and developing the latent charge image by applying oppositely charged pigmented particles. The toner image is then transmitted to an image-receiving material, such as paper, where it is fixed. Thereafter, the recording element is cleaned by rinsing with a constant amount of developer and freed of the toner and residual charge. If pigmented developer liquids are used, the cleaning operation includes rinsing the recording element with developer liquid using a cleaning device, such as a cleaning blade of an elastic material or a rotating brush (see French Pat. No. 2,000,397), or alternatively by leading the recording element through a cleaning chamber (see DE-AS No. 12 37 901).
As indicated above, the central component of a cyclically operating electrophotographic copier is the recording element comprising a photoconductor drum or a photoconductor element having a photoconductive layer including an organic photoconductor, such as, poly-N-vinylcarbazole and trinitrofluorenone, which is applied to a flexible support comprising a polyester film on an aluminum layer. Additionally, photoconductive layers of inorganic materials, such as selenium, can be doped, and applied to a metal drum.
Typically, the individual process stations are arranged around the recording element. During the cleaning operation of the photoconductive layer, developer liquid from a supply container is pumped onto the surface of the photoconductive layer, distributed by means of a foam-coated roller, and then wiped off with the aid of an resilient cleaning blade adjacent to the photoconductive layer. If possible, the photoconductive layer should be wiped dry. The cleaning station is preferably installed at an elevated spot on the photoconductor path, so that the developer liquid flows back into the supply container situated beneath the recording element. (See, e.g., DE-AS No. 21 54 892, herein incorporated by reference).
In FIG. 1 of the attached drawings an arrangement of the process stations is illustrated in a schematic and simplified manner. Situated around a recording element 1, illustrated as a photoconductor drum, are a charging station 2, an image-wise exposure station 3 and a developing station comprising a developing electrode 6 and a developer liquid 4 in a developer container 5. After the transfer of the toner image to the image-receiving material 7, cleaning is effected at the cleaning station which can include a foam roller 8 and a cleaning blade 9 of solvent-resistant rubber. Using a pump 10, developer liquid is transported into the cleaning station and then flows downwardly along the end surfaces of the recording element and back into the developer container 5.
One disadvantage of the prior art cleaning performance is the loss by evaporation of some of the dispersing liquid due to the free fall of large quantities of developer liquid. These losses may be greater than the losses occurring via the image-receiving materials, especially at increased surrounding or instrument temperature when using aliphatic hydrocarbons as dispersing agents, which is the common practice. Furthermore, deleterious changes in the developer liquid are observed due to the cyclic cleaning and subsequent return flow in a free fall, resulting in a considerable reduction of the copy quality, caused by the loss of dispersing agent which disturbs the sensitive system of charged pigmented particles and additives.